The Department of Energy has confirmed that its oldest double-shell tank is actively leaking radioactive and hazardous chemical waste from its inner shell.
DOE made the announcement Monday after a video inspection of the area between the shells Sunday showed more waste in one place than a video taken Thursday showed.
"It's a very, very small volume," said Tom Fletcher, DOE assistant manager for the tank farms. Although there's no good way to measure the amount, it could be a couple of tablespoons of additional waste between the video inspections.
Tank AY-102 is the first of Hanford's double-shell tanks known to have leaked waste from its inner shell.
The Hanford nuclear reservation has 28 double-shell tanks that are being used to hold waste from older single-shell tanks, many of which have leaked in the past. Together, the two types of underground tanks hold 56 million gallons of radioactive waste left from the past production of plutonium for the nation's nuclear weapons program.
Tank AY-102 is a year or two past its 40-year design life. However, waste will need to continue to be stored in at least some of the double-shell tanks until all the waste is treated for disposal, which may take another 40 years.
The waste is not believed to have leaked from the outer shell, which serves as secondary containment for the tank, into the soil beneath it. No waste has been found in the leak-detection pit beneath the tank, DOE said.
Material first was discovered in the 30-inch space between Tank AY-102's shells in August, leading to more checks. After videocameras were lowered through 10 risers, or pipes that give access to the area between the shells, three suspicious spots were discovered in a survey of about 95 percent of the space between the tanks.
One spot, a mound measuring 2 feet by 2 feet by 8 inches, now is believed to be soil. It could have fallen into the space between the shells during construction repairs to the ventilation system, Fletcher said.
But two spots on near opposite sides of the tank are radioactive waste, Fletcher said. Remote-controlled sampling devices were modified and sent into the area between the tank's walls to take several samples of the material. Analyses reviewed by a panel of experts and senior managers confirmed the two spots hold waste consistent with what is in the tanks.
It's more probable than not that the bottom of the inner shell is leaking in one place, with the waste coming out in two places in ventilation channels in the space between the shell, Fletcher said. Tank AY-102 holds waste that generates heat, and the ventilation system is used to help cool it.
Just one of the spots is increasing in size. It now covers about three square feet of the 600-square-foot floor of the outer shell and is less than a half-inch thick. The second spot covers an estimated 40 square feet and is less than a quarter-inch thick.
A review of the tank's history has shown there were a number of difficulties with its construction, Fletcher said. It was the first double-shell tank built, and 36 percent of its welds were initially rejected as not meeting quality standards. The welds were repaired and inspected before the tank was put into service in about 1971.
When the second double-shell tank was built, Tank AY-101, the weld rejection rate dropped to 10 percent.
DOE is planning next to inspect the six double-shell tanks that have similar construction and operating history to Tank AY-102, Fletcher said. Inspections are being accelerated and expanded, but it could take up to six months to finish videocamera inspections of them. Instruments in the tanks' risers will have to be removed to insert the videocameras and then reinstalled.
At Tank AY-102, DOE and its contractor Washington River Protection Solutions will continue videocamera inspections twice a week. It also will continue to monitor liquid levels inside the tank and the space between its shells, which can detect only large changes in volume.
DOE will work with its regulator, the state Department of Ecology, on longer-term plans for the tank, Fletcher said.
One option is to empty the tank, which has a capacity of about 1 million gallons and holds 850,000 gallons of waste.
But that has to be considered in context with what it will mean for managing the total double-shell tank space, which limits the amount of waste that can be removed from single shell tanks until the vitrification plant starts operating to treat waste for disposal. The budget also will have to be considered.
"It's all a balancing game," Fletcher said. Tank AY-102 now is essentially operating as a single-shell tank, he said. Some of Hanford's original single-shell tanks date back to World War II.
He also wants to consider the path forward in connection with DOE plans for mixing and sampling waste in double-shell tanks to allow it to be delivered in large batches to the vitrification plant, possible starting in 2019. Mixing the waste in 1 million gallon tanks to produce five batches that each meet the criteria set for treatment at the plant will be a challenge.
The Ecology Department has not seen the latest reports on Tank AY-102, "but obviously this is not great news," said spokesman Dieter Bohrmann. However, it was somewhat expected after DOE said earlier this month that preliminary results of sampling tests showed some of the material between the tank's shells was consistent with the tank's contents, he said.
Gov. Chris Gregoire said in a statement last week that the preliminary results of the DOE investigation were concerning and were another reason the state cannot afford any more delays in the construction and operation of the vitrification plant.
"Already, waste has been sitting in these double-shelled tanks past the tanks' life expectancy," she said.
"I have had conversations with DOE Secretary Steven Chu about my concerns and am confident he understands the importance and time sensitive nature of this issue," she said. "He has hired some of the most talented individuals, capable of tackling the tough challenges that Hanford cleanup presents."